This invention relates to a light source module, more particularly to a light source module for projecting a predetermined beam pattern.
The use of low wattage high intensity discharge (HID) lamps for automotive forward lighting is well established. All of the major lighting companies have such products in the market place. These types of lamps have been introduced in the automotive market in recent years and offer more light on the road for improved nighttime visibility. The increasing popularity of HID lamps results from the advantageous properties of these lamps compared to previous filament lamp. HID lamps have lower power consumption, higher luminosity and a longer lifetime than conventional filament lamps. High intensity discharge lamps have a very small size with a small discharge volume with electrodes extending into the discharge volume. The arc gap between the electrodes inside the discharge volume is only 3-4 mm. Therefore such HID lamps may be regarded as point-like light sources. If HID lamps are implemented in an automobile headlamp, special care has to be taken in order to provide for the required illumination pattern and to avoid glaring effect. The illuminating beam pattern of automotive headlights using gas-discharge light sources is determined by UN standard E/ECE/324 Addendum 97: Regulation No. 98 comprising uniform provisions concerning the approval of vehicle headlamps equipped with gas-discharge light sources. This standard has to be applied by all manufacturers who produce complete lamp assemblies. In order to meet the requirements set by the standard, the HID light sources have to be positioned and fixed very precisely relative to the reflecting mirrors. This requires exceptionally high accuracy for interfacing the light source and the reflector of each headlamp assembly.
U.S. Pat. No. 6,860,776 discloses a method for producing a lamp unit for an automobile headlight including a high pressure discharge lamp set and fixed to a reflecting mirror. In this method, the light emitted by a point-like light source (HID lamp) and reflected at a reflecting surface of the reflecting mirror is detected in order to determine a position for setting and fixing the light source. The position for setting and fixing said light source is defined by a position of the point-like light source, in which the reflected light is the maximum. In this way, a focal point of an elliptical mirroring surface can be found and the point-like light source may be positioned and fixed at this point. Lamp units assembled this way will have a maximum of output light intensity but will not necessarily fulfill any of the requirements set in existing standards.
Due to the diverse technologies incorporated in an automotive headlamp, e.g. lamp, electronics and optics technologies, most manufacturers produce only a part of the headlamps representing a technology. Then these main parts have to be assembled at another manufacturer. In order to meet the requirements for providing a predetermined beam pattern defined by the above standard, all main parts manufactured individually are standardized as well. UN standard E/ECE/324 Addendum 98: Regulation No. 99 comprises therefore uniform provisions concerning the approval of gas-discharge light sources for use in lamp units of power-driven vehicles. This standard makes provisions in order to define tolerances of the geometry, color, switch-on and switch-off behavior and intensity of gas-discharge light sources. The governing idea was that if all of the main parts of an automotive headlamp meet the requirement of these international standards, the assembled headlamp would also provide an illuminating beam pattern according to the above-mentioned standard. In practice however, implementation of this is not easy or requires high precision manufacturing, which results in high costs. It frequently occurs that the individual parts do not meet all requirements of the standards and even if the individual parameters are within the prescribed range, the resulting headlamp may have a light beam pattern, which does not meet the provisions of the standard due to assembling failures or coincidence of extreme tolerances. U.S. Pat. No. 5,945,776 issued to Koster et al. discloses a motor vehicle headlamp having a lamp aligned in a reflector with standard parts and suggests the use of special reference means on the reference surfaces in order to accomplish proper optical alignment.
Contemporary HID automotive headlamps have three main components that are standardized and optimized independently. These are the HID light source, its driving electronics and the optics reflecting and focusing the beam. Optical alignment of the arc position inside the HID light source, as well as positioning of the elements of the optical system, such as lenses, baffles, apertures is done independently, so that variability in light source and optics geometry affects final beam performance of the headlamp considerably.
Due to the standardized light source, no revolutionary optical approaches can be used in the design of projecting optics; in this way efficiency of the optical system is moderate and frozen according to the technology available at the time of standardization. The design of driving electronics is also closely coupled to the characteristics of the standardized light source used in the headlamp, and small deviations in light source characteristics of different manufacturers within the limits of standards cannot be handled by the system, which may cause system reliability problems. Due to the limitations in the designs of the individual components, and little variability allowed by the standards, cost of the contemporary headlamp is high, and its performance is also highly limited. Replaceable concept of interfacing of the individual components reduces system reliability. In case of failure no safe method exists to judge if reliability of other components are affected or not. In order to gain market share for the HID headlamp units in vehicle related or any other applications the cost of the system has to be considerably reduced, and its reliability increased.
There have been some approaches to increase system compactness and reliability of an HID headlamp system. D1 type lamps already include the igniter part of the driving electronics in the base portion of the HID light source. However, interfacing and statistical variability problems, as well as limitations for cross optimization are not solved by this approach either. The overall performance of the system remained basically unchanged, and a further increase of costs rather than cost reduction can be observed.
Thus there is a particular need for an HID headlamp system, in other words an HID Light Source Module (HID LSM), in which an HID light source, its driving electronics and elements of a projecting optical headlamp form a complex system, the elements of which do not necessarily comply with all of the requirements of the special standards for these elements, which however generates a predetermined projected beam pattern in the space or on the surface to be illuminated. The predetermined beam pattern may be a projected beam intended for automotive use, i.e. a beam pattern according to regulation R98, regulations defined for Advanced Forward Lighting applications, fog lamp standards, etc; for any other vehicle related applications including airborne or nautical ones, search light, working light or any other auxiliary beam illuminator applications, optical fiber pumping, or commercial lighting applications.